Much commercial mining today is accomplished by means of heavy machinery. This machinery often includes a large wheel or drum which is rotated while being driven into the face or surface of the coal or other mineral bearing wall being mined. Located about the periphery of the wheel or drum are a number of angularly spaced outwardly extending members called attack tools. Each of these attack tools has a hardened tip portion which engages or attacks and dislodges the coal or other mineral. The hardened tip of an attack tool can comprise an integral part of the tool, or as is more common, a replaceable insert which is soldered or brazed in place in a socket or cavity on the end of the tool. These attack tools, as they are the work engaging portion of the machine, are subject to significant wear, making tool wear an important problem for a number of reasons including its impact on the mining operation and also on the safety and economic considerations thereof.
Tool wear affects a number of operational parameters including the amount of energy consumed in mining, the product size, machine wear and tear and the main frame mass needed to advance the mining machine into the coal, as well as safety concerns such as the amount of respirable dust created by the mining process. Importantly, as the attack tools begin to wear, and more particularly, as the inserts at the tips thereof begin to wear or dull, the force required to drive the machine forward, called the normal force, can increase relatively quickly and abruptly. The normal force affects such parameters as the machine advance rate and depth of cut, which in turn affect the other parameters mentioned, making it critical to minimize the normal force in the mining operation. Dull or worn attack tools additionally tend to pulverize the coal rather than cut the coal, thereby causing higher levels of respirable coal dust which is one of the major causes of Black Lung disease.
Tool wear also results in machine downtime for changing the attack tools. It has been estimated that the downtime for the average longwall mining machine can cost as much as $200 per minute. If a mine runs three shifts a day and a longer lasting, more effective attack tool requiring fewer tool changes can save ten minutes of downtime per shift, the downtime savings would be $6,000 per day. This savings could be well over one million dollars per year in downtime alone. In addition, such operating parameters as the energy consumption of the machine and penetration rates improve and the health and wear and tear factors mentioned above also improve. Reducing the wear and tear on the mining machines additionally produces the benefit of reduced maintenance costs for the mining equipment.
Numerous mining attack tools having a variety of shapes, material compositions and tip configurations have been tried and used in the coal and mineral mining industry. One such known mining attack tool presently used in the coal industry has a steel tool body, usually of 4140 type steel or a tool steel such as S-7, the tool body having a socket in the tip thereof into which an insert, usually of tungsten carbide, is brazed in place. There are two known standard shapes for inserts used with these tools one being a pointed conical shape and the other a flat or disc-like shape. Although these shapes are standard in the industry, they both tend to wear or dull relatively quickly, resulting in the problems and reduced effectiveness discussed above.
In recent years some thought has been given to hardening inserts for the tips of mining attack tools by the use of diamond compacts. One such type of diamond compact is disclosed in Hall et al U.S. Pat. No. 4,604,106. This composite polycrystalline diamond (PCD) compact was disclosed for use in cutting, machining, drilling and like operations. Rock bits (which operate essentially in a rapid up-and-down motion) were also contemplated in the Hall invention. A 1984 patent issued to Campbell, U.S. Pat. No. 4,481,016, also discloses a method of making inserts suitable for attack tools or drill bits. This method describes fragmenting an abrasive compact into a plurality of discreet, non-segmental fragments. The abrasive compact in Campbell could be cubic boron nitride or diamond particle. The particular geometric shapes disclosed in the prior art include a rounded tip with steep sides such as disclosed in Hall, and a pointed conical tip as disclosed in Campbell. However, testing results show that both the rounded tip and the steep sides of Hall and the pointed conical tip of Campbell suffer from a number of deficiencies and do not substantially reduce the wear of a mining attack tool.